Embodiments of the subject matter disclosed herein generally relate to thrust bearings, and more particularly, to a magnetic thrust bearing for a turbo machine.
Turbo machines, such as turbo expanders or compressors, may be used to facilitate the addition or extraction of energy from a process fluid. In a typical turbo machine, a shaft mounted impeller, or rotor, is supported for rotation relative to a machine stator. In order to counteract thrust forces in the rotating shaft which may be generated by interaction of the impeller and the process fluid, a turbo machine may incorporate axial magnetic bearings.
Unlike more traditional bearings such as roller bearings or fluid film bearings, axial magnetic bearings require no lubricant which could contaminate the process fluid. As a result, turbo machines incorporating axial magnetic bearings may be operated without a seal between the process fluid and the axial magnetic bearings. However, this may result in exposure of the bearing to harmful contaminants which may be present in the process fluid. For example, if natural gas is being processed, significant levels of hydrogen sulfide (H2S), carbon dioxide (CO2), water, etc. may be present. These contaminants combine with natural gas to form a mixture called sour gas which is particularly corrosive to the steel components of conventional axial magnetic bearings. Sustained exposure to sour gas often results in sulfide stress cracking of such components. This process may cause bearing components to wear out prematurely, or worse, fail catastrophically.
Accordingly, what is needed is an axial magnetic bearing which may be more readily exposed to potentially corrosive fluids and which may otherwise provide improved performance to the turbo machine in which it is installed.